1. Technical Field
The present invention relates to a target recognition apparatus which recognizes a target by using information from a radar sensor and an image sensor.
2. Related Art
Conventionally, various target recognition apparatus are used for, for example, driving support of a vehicle. The target recognition apparatus recognizes various targets existing around the vehicle by using a radar sensor and an image sensor.
A millimeter-wave radar, which is a radar sensor, receives a reflected wave, which is generated when a radar wave is reflected from a target, by a plurality of antennas, and determines the direction of the target, which has reflected the radar wave, by using a phase difference Δφ generated between received signals of the antennas. However, Δθ=θ0 (|θ0|<π) and Δθ=θ0±2nπ (n=1, 2, . . . ) cannot be distinguished from each other due to periodicity in phase.
Hence, if a target exists within an azimuth range (basic detection area) corresponding to a range in which a phase difference Δθ meets −π<Δθ≦+π[rad], the direction of the target can be correctly detected. However, it is known that if a target exists outside the basic detection area, that is, within a range in which the phase difference Δθ meets Δθ≦−π or Δθ>π, the direction of the target is erroneously detected such that the direction of the target is apparently in the basic detection area.
JP-A-2007-263986 discloses a method for preventing such erroneous detection due to phase folding. According to this method, the position of a target candidate detected by radar is verified by a camera. If a target corresponding to the detection result of the radar is recognized, the detection result of a millimeter-wave radar is determined as true (a real image). If a target corresponding to the detection result of the radar is not recognized, the detection result of a millimeter-wave radar is assumed as a virtual image due to phase folding. In this case, target recognition using a camera is performed again for the direction (position) outside a basic detection area where a real image is expected to exist. In consequence, if a target exists, the expected position is used as a target position.
However, according to the apparatus disclosed in JP-A-2007-263986, if erroneous recognition is caused at the camera side, a virtual image (ghost) due to phase folding is erroneously recognized as a real image. Hence, stable recognition results cannot be obtained.